1. Field of the Invention
The present invention relates generally to a wafer positioning method and apparatus, and more particularly to a wafer positioning method and apparatus for a wafer with a notch.
2. Description of Related Art
An ingot such as silicon which is a material for semiconductor element is sliced into wafers by a cutting apparatus such as a slicing machine, and then the peripheral edge of the wafer is chamfered by a wafer chamfering apparatus.
In the wafer chamfering apparatus, the wafer is held on a rotary wafer table, and the peripheral edge of the rotating wafer is pressed against a rotating grinding wheel so that the wafer can be chamfered.
To accurately chamfer the wafer by the above-mentioned chamfering apparatus, the center of the wafer must correspond to and be fixed to the center of the wafer table when the wafer is mounted on the wafer table.
In the case of the wafer with the notch, the wafer must be fixed so that the notch can be positioned in a predetermined direction.
For this reason, the wafer chamfering machine is usually provided with a wafer positioning apparatus. The wafer is positioned by the wafer positioning apparatus, and it is fixed on the wafer table.
The conventional wafer positioning apparatus, however, has a disadvantage described below. It is unable to automatically position the notch, although it is able to automatically position the center of the wafer. Hence, a pre-alignment apparatus must be additionally provided to set the position of the notch.
If the pre-alignment apparatus does not correctly set the notch or if the notch is displaced during transportation of the wafer, the wafer is fixed on the wafer table with the notch being displaced. Thereby, the wafer cannot be chamfered accurately.